Safety paper and method of making same



Patented Jan. 9, 1940 SAFETY PAPER AND IMETHOD OF MAKING SAME 7 No Drawing. Application June '20, 1936,

Serial No. 80,34

15 Claims. (01. ill-67.95)

UNITED STATES PATIENT ioFFIcr:

- This invention relates to safety paper, including any fraud-preventing writing material made of paper or other substance or composition adapted for printing or lithographing or for the inscription of writing thereon and for use, for example, in the manufacture of checks, drafts, bonds, stock certificates; or other instruments, which it is desired to have protected against fraudulent alteration. This invention also relates to methods of making such paper.

Heretofore, chemically-treated safety paper (as distinguished from safety paper prepared with mechanical protectographs; etc.) has depended upon the incorporation of various colorless or suitably masked chemical substances in or on paper, in the form of a uniform application or in the form of printing or other indicia of voiding character, which react with. ink eradistroyed by the application of the eradicator, the

protective feature comes into play in the form prominent 'on the paper wherever the eradicator is applied and which is difllcult to obscure and therefore acts as a warning that the paper has been tampered with.

,I-Ieretofore safety paper has also beenmanufactured by'applying thereto asprinting, as a ,design or otherwise, alight coating of a colored delible material such as a fugitive dyestufi' as by pantographing or embossing which material is adapted to be removed-upon either chemical or mechanical erasure. Here, again, the safety features lie not in preventing the removal of the original writing but in producing telltale marks or disfigurations caused by local removal of the colored delible material, sothat new words or figures written on the document will be recognlZBd by the disfiguration of the background therefor.

Moreover, it has h retofore been proposed to incorporate a ferrocya de in safety paper which nate.

eradicator is applied to the original legend on the safety paper.

It is a purpose of this invention to improve:

great stabllity that the color thereof cannot be destroyed by known commercial ink eradicators and is extremely resistant to any'chemical means of eradication that is compatible with the paper on which the writing appears.

Features of this invention relate both'to the materials that are used and to the manner of theiruse. Features of this invention also relate to new and useful protective devices that give new and more perfect protection against fraudulent attempts at alteration of instruments.

It is a feature and advantage of one method of practicing this invention that it may be practiced in connection with the ordinary'ink which is in general use at the present time when applied to paper in the ordinary way. According to this invention, an ingredient of ordinary ink is chemically "fixed in a novel way so that the resultant writing comprises a substantially indelible colored substance.

- 'Writing ink in general use at the present time contains gallo-tannic acid. iron in the form of ferrous sulphate, ferrous chloride or the like, an

acid such as sulphuric acid or hydrochloric acid,

a dye (e. g., blue or black) and binders of various sorts such as gum tragacanth or gum arabic. The color of the ink is due to the dye and to the subsequent formation of black iron gallotan- However,such. ink is not indelible but may be readily removed by. several well-known chemical eradicators, leaving no visible trace thereof. v

Ink eradicators in use at the present time are of various diflerent types. The most commonly used eradicators have a chlorine bleach as their basis. Another type of ink eradicator has potassium permanganate as its basis. The latter eradicator is normally followed in actual use by- It is a serious objection in connection with the chemical method of safety paper protection heretofore practiced wherein use is made of the re.- action between chemicals and subsequently applied eradicators to produce stains or disfiguring marks, that the chemicals used are not reactive with all types of eradicators to produce prominently visible telltale marks. Thus,- there are sensitive chemicals which become prominently colored upon the application of common chlorine bleach but which are not sensitive to an ink eradicator having potassium permanganate as a basis. It is an advantage of this invention that the safety feature of safety paper embodying this invention is not dependent upon the type of ink eradicator that may subsequently be applied to the paper or upon any other treatment which is applied subsequently to the paper. It is an advantage of this invention that writing is permanently fixed to the paper in the form of a colored compound which is substantially indelible regardless of the type of eradicator which may be applied to the paper in attempting to erase writing thereon.

It is a further feature and advantage of certain methods of practicing this invention that an ingredient of writing ink is caused to enter" into a substantiallyindelible colored compound, the color of which is substantially different from the color of the inkthat is applied to the paper. Thus, forexample, according to this invention, safety paper may be treated with a substance which reacts with an ingredient of ordinary blueblack writing ink to form a substantially .indelible compound which, for example, may be red. Thus, for example, compounds such as an dipyridyl and ortho-phenanthroline from substantially indelible red compounds with an iron ingredient of ink. The original intense blue-black color of the writing ink-willsubstantially completely maskthe red color of the indelible compound until such time as the ink is treated with a chemical eradicator. When the eradicator is applied, the blueblack colorof the ink afforded, for example, by the iron gallotannate and/or dye, will disappear, leaving the original writing traced in a permanent red color, for example. The telltale tracing of different color not only gives warning that the paper has beentampered with but also renders it practically impossible to erase or mask the colored lines or to conceal the attempted alteration.

Chemicals. are described herein which can be used to fix ingredients of ink as substantially indelible colored compounds according to this invention and which are substantially stable even after long standing or exposure to light, and do not decompose with the formation of decomposition or oxidation products which undesirably or prematurely-discolor or stain the paper in any way. Heretofore great diiiiculty has been encountered in the use of substances which produce a stain .upon treatment with an eradicator due to the fact that such stain-producing substances decompose prematurely to an undesirable extent discoloring and spoiling the paper. Such dimculties are avoidable in the practice of this invention. Moreover, as aforesaid, the colored compounds that are formed in the practice of this invention are of such stability that they are highly resistant to acid or alkaline, or to oxidation or reduction conditions which are compatible with the paper on which they appear. The telltale colored tracings formed in the original writing cannot be removed except with the greatest difficulty.

Other features and advantages of this invention will be apparent from the following illustrations'of safety papers embodying this invention and methods of making the same.

in a preferred method of, practicing this invention, the iron which is contained in ordinary writing ink is caused to be substantially indelibly fixed upon safety paper by incorporating with safety paper organic chemicals of the character mentioned below, which form compounds with iron in ink that are not only colored but also are of such stability as to be substantially indelible. In referring to the colored compounds as being indelible", it is meant that the compounds are highly resistant to chemical eradicators such as the acids and bleaches that are used to remove the color of ordinary delible ink of the character aforesaid, for example.

By way of illustration, a safety paper can be made proof against alteration by incorporating in or applying to the surface of the safety paper about 5% or more of ortho-phenanthroline. This substance can be incorporated in or applied to the surface of the paper in any desired way. This substance is insoluble in cold water but forms a soluble hydrate and may thus be regarded as being water-soluble to a certain extent. It can be incorporated in the safety paper by mixing it with paper stock in the stock heaters, for example. It can also be applied by mixing it with water and spraying the mixture on the paper, by pass-. ing the paper through a bath of the mixture, by passing the paper through squeeze rolls moistened with the mixture, etc., as may be preferred. The substance can be applied continuously or discontinuously in or on the paper and may be in the form of printing or otherwise, although it is normallypreferable to apply the material continuously throughout the surface of the paper so that any writing placed upon the safety paper will be indelibly fixed in its entire extent and preserved against any attempt at alteration. Orthophenanthroline is soluble in organic solvents, e. g.. ethyl alcohol, and it can be applied as a solution in an'organic solvent although .such method of application is, in the usual case, relatively more expensive than applying the material mixed with water.

Ortho-phenanthroline is substantially colorless and when it is applied to safety paper its presence is not noticeable. However, after ink containing iron has been applied to the paper, e. g., in the form of a legend such as a signature, attempts'to remove the ink thus applied to the treated safety-paper will show that the orthophenanthroline has formed a compound with the iron in the ink which is of a permanent red color. The ink may be the usual blue-black iron gallotannate ink containing the iron compounds referredto above or may contain some other water soluble iron compound together with gallo-tannic acidand/or a dye. While the original blue or black color of the ink may be substantially completely removed by the application of an eradicator, the red color of the compound persists, as the color of the colored compound is much more resistant to ink eradicators than is the delible ink and is substantially indelible. Prior to the treatment with the eradicator, the black iron gallotannate and/or dye conceals the red color of the compound formed by the ortho-phenanthroline reacting with the iron of the ink, and the writing has substantially the same appearance that it would have had if it had been applied to ordinary writing paper. However, if the delible blue or black color of the iron gallotannate and/or dye is removed by chemical erasure, the indelible red color of the reaction product will'persist, as it is highly resistant to all chemical methods of erasure. Thus the paper will have incorporated therewith as a legend or otherwise a material comprisinga delible colored portion and a substantially indelible colored portion, the colors of thedelible and indelible portions being different.

' Substantially complete and foolproof sai'ety'paper protection-isthus 'afl'orded. 1

While specific piention has been made of the substance ortho-phenanthroline, other chemicals may be employedln .the practice of this invention 19 to iorm stable colored compounds with the iron in ink. 'rThus aa' fdipyridyl, am" pyridyl) quinoline, out diqi'iinolyl, and (a' pyridyl) pyrroi may also be used jas above described in connection with ortho-phenahthroline. These substances fix the iron in writing hi the. form of colored compounds, the color of which cannot be removed from. the paper.-

While m dipyridyl, .ortho-pherianthroline,

. aim pyridyl) ,quinoline,-ma' diquinolyl, and

um' pyridyl), pgrrol possess 'diflerent molecular compositions, they have acertain common conflsuration or group, as will appear from the following iormulae -twhich is believed to show the structures of these compounds as far asit is possible to do so by conventional formulae):

a Orthopbcnanthrolinod ac Dipyridyl Each of the above compounds contains (enclosed 75 in dotted liner for clarity) the group N-C-C-N,

each' of the reactive nitrogen atoms attached to the adjacent carbon atoms of the group being in a separate heterocyclic ring structure. It is believed that this group to which attention has 'been called is responsible for the association of o a substance in which it appears with iron in the ink to form stable compounds. In any event,

substances having this group have this property.

the salts, homologues, and derivatives of an. dipyridyl, ortho-phenanthroline, a(u'.py1'i- 1o dyl) quinoline, aa' diquinolyl, and so" pyridyl) pyrrol having the N-C-C-N group above referred to are especially desirable reagents which have the property of forming with iron compounds stable colored compounds resistant to removal by 15 chemical ink eradicators. Moreover, any substance containing an N-G-C-N group, each of the N atoms attached to the adjacent carbon atoms being in a separate ring structure, is adapted to form stable colored compounds with 80 iron compounds, and thereby, when previously incorporated in safety paper, fix a legend, for example, inscribed in ink containing iron upon the safety paper, so that the legend will be highly resistant to removal by chemical reagents? 25 The number of atoms contained in the aforesaid molecule apart from NCC--N group is largely immaterial except that in general it may bestated that the larger the molecule is, the more stable will be the colored compound which the $0 compound containing the configuration mentioned will form with iron in ink. It is preferred that the -molecular weight of such substance be at least 132, the molecular weight of u(' pyridyl) pyrrol mentioned above. The color of the coma pound that is formed with iron will also vary to some extent with the molecular structure associatedwith the NC-C-N group.

" In indicating the group N-C-C-N, no attempt is made to show valence bonds (although 40 in the foregoing iormulaeat least one ofthe nitrogen atoms is attached to one of the carbon atomsby a double bond) but merely to show a certainmolecular group which, is regarded as responsible i'or the property or "characteristic 5 of substances containing such group or configuration, of entering into stable molecular association with iron such as the iron compounds in ink to roduce stable colored compounds.

Substancesoi' the character above mentioned, namely, having the NCCN group wherein the N atoms attached to the adjacent carbon atoms are each in aseparate ring structure are not only reactive with water solu le compounds of iron, e. g., in iron gallotannate ting ink, but u arealso reactive with water soluble compounds of'nickeland cobalt such 'as the nitrates andchlorides of these metals. Thus when a chemical of the character aforesaid having an NC--C-N group is incorporated with safety paper, an ink on containing nickel or cobalt or both will, when applied to the paper, form a substantially indelible colored compound. The compound thus formed with nickel, or cobalt, while being. similar in character to the indelible iron compounds men- 35 tioned above, are not as stable nor as desirable 1 for other reasons, but nevertheless are of value. I Such an ink may be afforded by dispersing in a liquid carrier a highlycolored dye (of which many areik'nown; for example Soluble Blue 70 (Schultz'No. 539), Acid Violet 4 BL, Acid ,Green.

G6, etc., together with some water soluble;com-' pound of nickel or cobalt-or both, such as the -chlorides, nitrates, and the like. In such case, g the dye would ordinarily be readily removed by 15" the action of a chemical ink eradicator, such as an eradicator containing a bleaching agent, but the colored compound. resulting from the reaction between the substance having the NC-C--N group (incorporated with the paper) and the nickel or cobalt or both (applied in the ink) will remain and will preserve substantially indelibly the form of the mark made by the ink (e. g., a legend) on the safety paper. The dye,ifadyeisused,canbeofanydesiredcolor and preferably a color is to be selected which contrasts with the color of the reaction product safety paper wherein an ink-fixing compound occurs in the body of the paper or is applied to the surface thereof in any way. Approximately 1% to approximately 5% on the weight of the paper of the ink-fixing reagent'is usually sufficient to give a stable colored compoimd upon combining with iron (or nickel or cobalt) in ink that is applied to the treated paper. Thus the original tracing of the pen upon the paper becomes per-- mauently fixed and rendered incapable of eradication by known chemical means.- Of course. additional amounts of ink-fixing reagent tend to increase the prominence and indelibility of the color produced with iron in ink. Moreover, as the intensity of the color which iron (or nickel or cobalt) forms with the chemicals which may be used as ink-fixing reagents varies to some extent, somewhat more ink-fixing reagent may be desirable in connection with some reagents than with others.

If the particular ink-fixing reagent which it is desired to use is soluble in water, a simple and convenient way of applying same to the safety paper is to'rim the'paper through a bath of the reagent and then pass the paper between squeezing rolls. The bath may be, for example, of a concentration of 5% to 20% of ink-fixing compounds, as such concentration has been found in the usual case to incorporate inthe paper about 1% to5% of thecompoundonthe weight ofthe D D F- If the particular ink-fixing reagent which it is desired to use is insoluble in water, the material can be appliedin the form of a suspension in water by adding the material in desired proportion to the stock thus incorporating the material in the paper or it may be applied in the form of a suspension in anypf the other ways,

that a solution may be used. Moreover, a waterinsoluble ink-fixing reagent can be applied to the paper, dissolved in some other solvent than water, e. g., alcohol. The foregoing remarks are applicable to the incorporation with safety paper of ink-fixing reagents which are either solid or liquid. While either solids or liqu ds may be used in the practice of this invention, it is preferable that the reagent used be solid and, if a liquid, that the liquid be sufliciently nonvolatile toremaininthepapertoproducethedesired efiect. I

The application of the ink-fixing reagent in or to safety paper embodying this invention may be performed as a separate step or combined with other steps that are normally incident to the manufacture of paper. Thus the material may be applied during tub sizing. Moreover, a solution or suspension of ink-fixing material may be applied in embowng or pantographing safety paper. Alsotbereagentcanbesprayedontbe web of the paper or applied by means of water boxes on calender rolls. In general, any method of incorporating an ink-fixing reagent in the safety paper or on the surface thereof may be used in the practice of this invention.

, Especially complete protection is afforded when an ink-fixing reagent. e.- g., of the character aforesaid, is incorporated with safety paper which in addition carries a colored material, such as a fugitive dyestuif, which is adapted to be removed by chemical erasure. Thus, for example, an ink containing the reaction product of an ink-fixing reagent of the character aforesaid with a water soluble compound of iron, cobalt, or nickel, together with a dye may be made up and applied to paper carrying the fugitive dye superficially.

, Alternatively, such ink-fixing reagent may be incorporated with safety paper in addition to a superficial application of delible colored dye substance and thereafter be written upon with a delible ink containing iron, for example. when a chemical eradicator is applied-to paper treated in the manner aforesaid, the color of the delible superficial dyestuff and the normal color, e. g., blue-black, of the writing or other legend on the paper will be bleached out, leaving a colored indelible tracing of the original writing or other legend upon a bleached background; Colored delible dyestuffs adapted to be superficially applied over the surfam of safety paper are well known. For example, dyes may be used such as ...Metanil Yellow, Wool Orange, CroceinScarlet,

etc.

' Safety paper which has incorporated therewith an ink-fixing reagent may also embody in combination a reagent adapted to produce disfiguring stains or prominent indicia upon the paper when a chemical eradicator, is applied thereto. Such chemicals, many of which are well known, have their color affected by ink eradicators by change from a colorless to a colored condition, by intensincation of color, or by change of color. Such chemicalsarereferredtohereinasbeingadapted to develop a stain as an ink eradicator affects safety paper treated with such chemicals so asto result in what appears as a telltale stain. Thus, for example, a sensitive-chemical such as diphenyl amine dlpbenylamine sulphate, benzidine or benzidine sulphate may be applied to the paper in combination with an ink-fixing reagent ,of the character? herein described. Moreover, other stain-producinsmaterials, such as diand tri-aryl guanidines, e. g.,' di-phenyl-guanidine and tri-phenyl guanidine, and amino-aryl-thiasoles, e. g., z-amino-benzthiazoleqo-sulphonic acid and I 2-amino-p-naphthathlazole-7-sulphonic acid may The sensitive be used to apecial advantage.

chemicalwill produce a disfiguring stain upon the application of a chlorine bleaching agent thereto. However, such sensitive chemicals will be substantiallyunaifected by eradicators havabove that the ink-fixing reagents of which nlustrations have been herein given produce colstances such as lead ferrocyanide. The latter substance produces a blue discoloration when subjected to ordinary acids and likewise produces a. discolorationwhen an oxidizing eradicator containing potassium permanganate is used.

Conversely, an ink-fixing compound of the character herein dwcribed which forms with an ingredient of ink a colored compound that is substantially unaffected by oxidizing conditions may be used in combination with a substance adaptedto produce a disfiguring stain upon the application of an ink eradicator having a reducing action, such as mercury salts, mercurous sulphanilate being an example.

Further in the practice of this inve tion, an ink-fixing reagent of the character h rein described may be incorporated with safety paper,-

together with a colored delible material such as a fugitive dyestuff and a stain-producing chemical sensitive to eradicators.

While mention has been made of the use in the practice of this invention of substances which react with iron in ink to produce colored substantially-indelible compounds, it is to be under stood that the term iron in ink is to be construed broadly. Iron in ink may comprise entirely ferrous iron as freshly applied to paper and then become gradually oxidized to ferric iron. A substance of the character aforesaid which reacts with iron in ink at any stage of its transition or in any form or chemical combination, is to be regarded as coming within the scope of this invention.

While this invention has been illustrated in connection with safety paper having incorporated therewith an ink-fixing reagent so that an ingredient of ink when applied to the paper will form a substantially indelible colored compound, it is also within'the scope of this invention to include a substantially indelible colored com= pound in ink prior to the application of the ink to the paper. Thus,'for example, the colored reaction products hereinabove mentioned could be used alone in an ink or could be added to an ink containing another colored substance'prior to applying the ink to paper. Thus, for example, ink could be made to contain a colored compound such as the compound formed between ferrous sulphate and ortho-phenanthroline or tzcz dipyridyl. Moreover, other colored reaction products between water soluble iron, nickel or cobalt compounds and a substance containing an NC--CN group wherein the N atoms are each in a separate ring structure, could be used. Due to the stability of such compounds, only a small amount would be necessary in the ink. If the ink also contains other colored ingredients, such as a delible dyestufi, for example. any attempt at chemical erasure of such an ink would only result in removing the color of the dellble portion thereof and the inde ible colored compound substance is used in addition to the stable col-. cred reaction product of the character herein described, it is preferable that the color of the delible substance be different from the color of the indelible substance, and that the color. of 5 the ink as "applied be due predominantly to the colored delible material. In such case, an ink can be afforded of any commercially desirable initial color which after application as a legend to paper will show a marked color change when a chemical eradicator is applied, but which thereafter remains. indelible both as to the secondary developed color and the form and shape of the original legend.

In the foregoing description, reference has 15 been made to fixing an ingredient of ink applied to safety paper by having incorporated with the safety paper a substance adapted to substantially indelibly fix the ingredient of the ink on the paper. 'In' this connection, ink applied to the 29 safety paper may be applied in the form of wrlting as inscribed with a pen or other writing instrument, e. g., signatures, figures, names, dates or other legends. All ink writings, designs, patterns, etc., are to be regarded herein as inscribed legends. I

When a delible ink is inscribed as a legend upon safety paper having incorporated therewith a material adapted to form a substantially indelible compound with an ingredient of the ink, the resulting legend will comprise two portions, namely, a delible portion and an indelible portion, and it is a feature of this invention that the indelible portion of the legend be selected so as to have a substantially different color from the delible portion. Thus, upon the application of an eradicator, the legend will show a marked color change, but will remain substantially indelible both as to the secondary developed color and the form and shape of the original writing. A as like result will, of course, also be obtained when a legend is inscribed upon ordinary paper with an ink containing a colored delible portion and an other portion of contrasting color which is substantially indelible. Thus a safety paper hearing a legend in-the form of ordinary writing or of an arbitrary or ornamental character, whether manually or mechanically applied, which is inscribed with a delible colored substance and a substantially indelible substance of contrasting as color, both substances exhibiting the form of the inscribed legend, is to be regarded as coming within the scope of this invention regardless of the method of application employed.

I claim:

1. Safety paper having incorporated therewith a substantially colorless substance whose molecular structure includes the atomic grouping N-CC--N, each of the nitrogen atoms attached to" the adjacent carbon atoms in said group being contained in a separate ring structure and atleast one of said nitrogen atoms being attached to one of said carbon atoms by a double bond.

2. Safety paper having incorporated therewith a substance whose molecular structure includes the atomic grouping NC--C--N, each of the nitrogen atoms attached to the adjacent carbon atoms in said group being contained in a separate ring structure and at least one of said nitrogen atoms being attached to one of said carbon atoms by a double bond, the-molecular weight of said substance being at least 132, and said substance being adapted to react with a water soluble compound of iron to use a caiored comm pound the color of which is more intense than the color of said substance.

8. Safety paper having incorporated-therewith a substance whose molecular structure includes the atomic grouping NC-C-N, each of the nitrogen atoms attached to the adjacent carbon atoms in said group being contained in a separate ring structure and at ieast'one of said nitrogen atoms being attached toone oi said carbonatoms. by a double bond, the amount of said substance,

atoms being attached to one of said carbon atoms by a double bond, and a material adapted to produce a stain upon the application of a chemical ink eradicating agent thereto.

5. Safety paper having incorporated therewith a substance whose molecular structure includes the atomic grouping N-C-C-N, each of the nitrogen atoms attached to the adjacent carbon atoms in said group being contained in a separate ring structure and at least one of said nitrogen atoms being attached to one of said carbon atoms by a double bond, and a colored delible material.

6. Safety paper having incorporated therewith a substance selected from the group consisting of ortho-phenanthroline, m'dipyridyl, aa'diquinolyl, em'pyridyb quinoline, eor'pyridyl) pyrrcl, and salts, homologues and derivatives 0! said sub stances having the group N-C-C-N, each of the nitrogen atoms attached to the adjacent carbon atoms in said group being contained in a.

separate ring structure.

7. Safety paper having incorporated therewith ortho-phenanthroline.

8. Safety paper having incorporated therewith py li 9. Safety paper having incorporated therewith m'diquinolyl.

10. Safety paper having incorporated therewith a colored reaction product between a substance whose molecular structure includes the atomic grouping N-C-G-N, each of the nitrogen atoms attached to the adjacent carbon atoms of said group being in a separate ring structure and at least one or said nitrogen atoms being attached to one of said carbon atoms by a double bond, and a compound selected from the group consisting of water soluble compounds of iron, nickel and cobalt;

mosaic ii. an ink comprising a colored reaction prodnot between a substance whose molecular structure includes the atomic grouping N-C-C-N, each of the nitrogen atoms attached to the adiacent carbon atoms in said group being contained in a separate ring structure and at least one of said nitrogen atoms being attached to one of said carbon atoms by a double bond, and a compound selected trom the group consisting of water soluble compounds oi iron, nickel and cobalt.

12, an ink comprising a colored reaction prodnot between a substance whose molecular structure includes the atomic grouping N-C-G-N, each of the nitrogen atoms attached to the adjacent carbon atoms in said group-being containedin a. separate ring structure and at least one or said nitrogen atoms being attached to one of said carbon atoms by a double bond, and a compound selected from the group consisting of water soluble compounds of iron, nickel, and cobalt, and adelible colored compound the color of which is substantially different from the color of-saidreactionproductandwhichimparts the predominant normal color characteristic to said ink.

13. A method or making safety paper which comprises incorporating with safety paper a substantialiy colorless substance whose molecular structure includm the atomic grouping N-CCN each or the nitrogen atoms attached tq the adjacent carbon atoms being contained in a separate ring structure and at least one of said nitrogenatomsbeingattachedtocneof saidcarbon atoms by a double bond.

14. A method of treating paper which comprises incorporating with paper a substance whose molecular structure includes the atomic grouping N-C-C-N, eachof the nitrogen atoms attached to the adjacent carbon atoms 0! said group .being contained in a separate ring structure, and thereafter applying to said paper a compound reactive with said substance to produce a stable colored compound. said compound being selected from the group consisting of water soluble compounds of iron, nickel, and cobelt.

I 15. A safety paper having incorporated therewith a substance whose molecular structure includes the atomic grouping N-C-C-N, each of said nitrogen atoms attached to the adjacent carbon atomsinsaidgroupbeingcontainedin a separate ring structure and at least one of said nitrogen atoms being attached to one of g said adjacent carbon atoms by a double bond. L. SIMONE. 

